Heat sensitive composition and thermal recording sheet containing the same

ABSTRACT

1. A THERMAL RECORDING SHEET WHICH CONTAINS THE PHENOL COMPOUND HAVING THE FORMULA   HO-(1,4-PHENYLENE)-C(-CH3)(-C5H11-N)-(1,4-PHENYLENE)-OH   AT LEAST ONE ORDINARILY COLORLESS OR LIGHT-COLORED LACTONE COMPOUND CAPABLE OF REACTING WITH SAID PHENOL COMPOUND UPON HEATING TO FORM A COLOR, AND A BINDER, THE PROPORTIONS OF PHENOL COMPOUND, LACTONE COMPOUND AND BINDER BEING 1-30% BY WEIGHT OF THE LACTONE COMPOUND, 45-   94% BY WEIGHT OF THE PHENOL COMPOUND AND 4-40% BY WEIGHT OF A BINDER, EXPRESSED BY DRY WEIGHT PERCENTAGE.

Nov. 5, 1974 yos FUTAKl E'I'AL 3,846,153

' HEAT SENSITIVE COMPOSITION AND THERMAL RECORDING SHEET CONTAINING THESMIE Filed July 2 1972 DE/VS/T) 0F GRCUND COLOR (40 6' AF 727?? ONE WEEKQ O 0.3 XI

1 l l l i l l l l l 1 I I l l 0 80 90 ,/00//0 /20 B0 /40 /50 COLORFORM/N6 WERE ("6'1 United States Patent 3,846,153 HEAT SENSITIVECOMPOSITION AND THERMAL RECORDING SHEET CONTAINING THE SAME KiyoshiFutaki, Isao Kohmura, and K020 Haino, Kyoto, Japan, assignors toMitsubishi Paper Mills, Ltd., Tokyo, Japan Filed July 24, 1972, Ser. No.274,618 Claims priority, application Japan, Aug. 5, 1971, 46/ 59,143Int. Cl. B41m /18 US. Cl. 11736.9 5 Claims ABSTRACT OF THE DISCLOSURE Inthe heat sensitive composition and thermal recording sheet comprisingcombination of a color forming lactone compound and a phenol compound,the compound having the formula Il-OsHu is used as said phenol compound,whereby excellent preservability and stability of the composition isattained.

The present invention relates to a heat sensitive composition whichcomprises combination of an ordinarily colorless or light-colored colorforming lactone compound and -a phenol compound. Furthermore, thepresent invention concerns a thermal recording sheet which contains saidcomposition.

'0. Fischer and F. Rorner already reported in Berichte der Deutschenhemischen Gesellschaft (Vol. 42, pages 2934-2935, 1909) that a colorforming lactone compound such as Crystal Violet Lactone reacts withphenols to form color and application of such reaction to thermalrecording sheet is disclosed in Japanese Patent Publication No.14,039/70. Besides said recording sheets, a great number of thermalrecording sheets have been proposed. However, for industrial utilizationthereof, the following requirements must be met; namely, (1) groundcolor of the sheet must be colorless or light color, (2) it must bestable for a long period of preservation at room temperature, (3) itmust rapidly form deep color at a certain temperature, e.g., atemperature of 70 C.- 200 C., (4) the color formed must be clear andfully stable against light and moisture, (5) it must have no smell andtoxicity and moreover -(6) it must be able to be economically produced.It is extremely difiicult to produce thermal recording sheet whichsatisfies all of the above requirements. The most difficult requirementis to improve preservability. This purpose may be attained by settingthe color forming temperature of the heat sensitive composition at ahigh level, but in this case a large amount of heat is required forrecording. Thus, a large amount of electric power is required forthermal pen or thermal printer and high speed recording becomesdifiicult. Therefore, such method is practically disadvantageous. On theother hand, when color forming temperature is set at a low level,recording can be carried out with a small amount of electric power. Inthis case, however, the stability of the part of the sheet where nocolor is formed is lowered and the possibility of color-forming duringpreservation increases. Therefore, such thermal recording sheet as beinghighly stable at room temperature and having a color-forming temperatureof as low as possible is desired, but it is very difiicult to produce aheat sensitive composition which simultaneously meets the above tworequirements. Practically, the thermal recording sheet is ofteninadvertently placed near a heater or other heat sources and therefore,special care must be given in handl-ing of the thermal recording sheetwhich has too low color forming temperature. Therefore, a thermalrecording sheet which rapidly forms color at a temperature of about -l00C. and is highly stable at room temperature has been desired forpractical use. To meet such requirements has been technically verydifiicult. In this connection, the color forming temperature has a closerelation with melting point of the compounds which constitute the heatsensitive composition. This fact will be explained with reference to thesystem comprising an ordinarily colorless or light-colored color forminglactone compound and a phenol. A color forming lactone compound and aphenol which are solid at room temperature are separately ground to aparticle size of less than about several microns in solvents which donot dissolve them with use of e.g. a ball mill. Thereafter, they aremixed and the mixture is applied together with a binder to a paper andis dried to obtain a thermal recording sheet. In this case, whenmono-phenols such as 4-tert.buty1 phenol (melting point: 9499 C.),u-naphthol (melting point: 9596 C.), B-naphthol (melting point: 119- 122C.), etc. are used, the preservability and stability of the thermalrecording sheet are low and not only it gradually forms color at roomtemperature, but it has the s-o-called phenol smell. Diphenols includecompounds excellent for thermal recording sheet and when4,4'-cyclohexylidene diphenol (melting point: C.) or 4,4-is'opropylidene diphenol (melting point: 156 C.) is used, such sheet ashaving clear thermal color formation and practically high stability canbe obtained. However, in case of the former compound, the color formingtemperature :is too high and in case of the latter compound, the colorforming temperature is sometimes also too high. Therefore, the recordingsheet having lower color forming temperature without damaging practicalstability and preservability has been demanded.

The inventors have made extensive researches to succeed in obtainingheat sensitive composition which meets said requirements. That is, thisheat sensitive composition comprises combination of at least one ofordinarily colorless or light-colored color forming lactone compounds,namely, Leuco Lactone dye and P,'P'-(l-rnethyl-normalhexylidene)diphenol having the following chemical formula,

The color forming lactone compounds used in the present invention meanthe ordinarily colorless or light-colored lactone compounds capable ofreacting with said phenol compound to form color. The representativeexamples of such lactone compounds are the following triphenylmethanel'actones, fluorans, benzofluorans, etc., but the present invention isnot limited to use of only these compounds.

Crystal Violet lactone, Malachite Green lactone, 3,3-bis (paradimethylaminophenyl)-6-aminophthalide, 3,3 bis (paradimethylaminophenyl) 6(paratoluenesulfonamide)phthalide, 3diethylamino-7-dibenzylamino-fluoran, 3-diethylamino 7(N-methylanilino)-fiuoran, 3-diethyl amino 7(N-methyl-p-toluidino)-fluoran, B-dimethylamino 6 methoxy-fluoran,3-diethylamino-6-methyl-7- chloro-fiuoran,3-dibutylarnino-6-methyl-7-chloro-fluoran,3-diethylamino-7-phenylfluoran, 3-morpholino-5,6-benzofluoran.

A method for producing the phenol compound used in the present inventionis disclosed in US. Pat. 2,535,014 (Dec. 19, 1950).

The general method for producing the thermal recording sheet of thepresent invention is as follows: The phenol compound as mentioned aboveand the ordinarily colorless or light-colored color forming lactonecompound are separately ground together with a binder in a medium whichdoes not dissolve said compounds by ball mill to obtain dispersionliquids. Then, these liquids are mixed. The mixture is applied to asubstrate sheet and dried. Alternatively, each dispersion liquid isapplied to a substrate sheet in order or one of them is contained in asubstrate sheet and the other is applied to the substrate sheet. Whenthe substrate sheet is paper, fine powders of both compounds may beincorporated into the paper at paper making step or one of them may beimpregnated in paper as a solution and the other dispersion may beapplied to the paper.

As the medium for the dispersion of the compounds, water or petroleumsare suitable. As the binder, water soluble high polymer compounds suchas polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, styrene,butadiene or acrylic latex may be employed in case of using water as themedium and terpene resins, cyclized rubber, etc. may be used in case ofusing petroleums as the medium.

Suitable amounts of the lactone compound, the phenol compound and thebinder are 13()% by Weight, 45-94% by Weight and -40% by weight (theseare dry weight percent), resepectively. If necessary, talc, waxes,surface active agents, defoaming agents etc. may be added to improveapplication state and recording state. Furthermore, a protective layermay be provided onto the heat sensitive layer to further improve thestability.

EXAMPLE 1 Liquid A G. Crystal Violet lactone 1 5% Aqueous solution ofhydroxyethyl cellulose (HEC BL-lS manufactured by Fuji Chemical Co.) 5Water 4.4

Liquid B P,P'-(lmethyl-normal hexylidene)diphenol 5 5% Aqueous solutionof hydroxyethyl cellulose Water 22 Said liquids A and B were separatelyground for 2 days in ball mill to produce two dispersion liquids. Then,the two were mixed and the mixed liquid was applied to an ordinary paperhaving a basis weight of 50 g./m. and dried. The amount of the appliedliquid was about 3 g./m. expressed by dry weight. Thus obtained thermalrecording sheet was stable at room temperature and the ground color ofthe applied layer was substantially white and rapidly formed blue colorat about 90 C. When a letter was copied with heating, a clear recordingof the letter was obtained.

For comparison, the following experiment was carried out. That is, inplace of P,P'-(1-rnethyl-normal hexylidene) diphenol in said liquid B,similar compounds mentioned in the following Table 1 were used.

Properties of thus obtained thermal recording sheet are shown in Table 2and FIG. 1.

TABLE 2 Density of Color ground color I forming Phenol temper- DensityColor Immediately After 1 compounds ature of color forming after Week atused C.) formed 3 speed production 40 C 145 1 25 Rapid 0.06 0.07

135 1 03 Slow- 0. 02 O. 02

100 1. 12 Rapui 0. 28 0.51

0.78 Slow 0.02 0. 02

90 1.12 Barn 0. l4 0. 26

1 Tem erature of the part of the sheet at which color was formed in ahigh density when the sheet was allowed to contact with a metal platehaving a temperature gradient.

2 The density was measured with the Macbeth densitometer (reflectiondensity).

FIG. 1 shows the relation between color forming temperature at whichcolor is formed in high density for a short period of time and densityof ground color formed after lapse of one week at 40 C. of thermalrecording sheets using various phenol compounds. In other words, itshows the relation between color forming temperature and stability(density of ground color after one Week at 40 C.). In this FIG. 1, whitedot indicates that the color forming speed was high (i.e.: quickresponse) and black dot indicates that the color forming speed was low(i.e.: slow response).

As is clear from Table 2 and FIG. 1, the recording sheet containing thepresent phenol compound (X) formed color at the preferred temperature ofrelatively lower temperature as compared with the recording sheetscontaining compounds (I) and (II). In case of other phenol compounds(HI), (IV), (V), (VI), (VII), (VIII), (IX) and (XI), the sheets formedcolor at a preferred temperature of relatively low temperature, but hadpractically fatal defects. That is, in case of the compounds (111) and(VIII), when liquids A and B were mixed, the liquid severely formedcolor and hence the liquid when applied to sheet caused formation ofdeep ground color, which was not practically desired. Furthermore, incase of the compounds (IV), (V), (IX) and (X), formation of ground colorimmediately after production of recording sheet was not so severe, butwith lapse of time (during preservation) the ground color was formed. Incase of the compounds (II), (VI) and (VII), the sheet obtained hadsuitable color forming temperature and good preservability, but thecolor forming reaction on application of heat occurred slowly and thesheet was not suitable for high speed recording. On the other hand, thecompound (X) of the present invention showed substantially no formationof ground color, had rapid color formation reaction and had excellentpreservability.

invention.

5 EXAMPLE 2 Example 1 was repeated except that 3-dibutylamino-6-methyl-7-chlorofluoran was substituted for Crystal Violet lactone toobtain an excellent thermal recording sheet which formed red color withheat in substantially white ground.

EXAMPLE 3 Example 1 was repeated except that 3-diethylamino-7-(N-methyl-P-toluidino)fiuoran was substituted for Crystal Violet lactoneto obtain an excellent thermal recording sheet which formed green colorin substantially white ground.

What is claimed is:

1. A thermal recording sheet which contains the phenol compound havingthe formula:

at least one ordinarily colorless or light-colored lactone compoundcapable of reacting with said phenol compound upon heating to form acolor, and a binder, the proportions of phenol compound, lactonecompound and binder being 130% by weight of the lactone compound, 45-94% by Weight of the phenol compound and 4-40% by weight of a binder,expressed by dry weight percentage.

2. A thermal recording sheet according to claim 1, having said lactonecompound and phenol compound in admixture applied on a substrate sheet.

3. A thermal recording sheet according to claim 1, wherein said lactonecompound and phenol compound are applied in separate layers on asubstrate sheet.

4. A thermal recording sheet according to claim 1, wherein either one ofthe lactone compounds or the phenol compound is contained in a substratesheet and the other is applied to said sheet.

5. A heat sensitive room temperature stable composition comprising thephenol compound having the formula:

and at least one ordinarily colorless or light colored lactone compoundcapable of reacting with said phenol compound upon heating to form acolor, said composition comprising 1-30% by weight of the lactonecompound,

15 4594% by weight of the phenol compound and 5-40% by weight of abinder expressed by dry Weight percentage.

References Cited 0 UNITED STATES PATENTS 3,539,375 11/1970 Baum 117-3683,451,338 6/1969 Baum 11736.8 3,466,185 9/1969 Taylor l1736.8 3,244,5504/1966 Farnham et al 117-368 25 3,666,477 5/1972 Golfe 117'-36.8

WILLIAM D. MARTIN, Primary Examiner B. D. PIANALTO, Assistant Examiner 0US. 01. X.R.

1. A THERMAL RECORDING SHEET WHICH CONTAINS THE PHENOL COMPOUND HAVINGTHE FORMULA